text highlighting css layouts

I was wondering if anyone can tell me why sometimes in css layouts it is difficult to select or highlight the page text? This obscurity is more prominent in IE6 than NS7 but when you try to select a small area of text in IE maybe it won't select but all of the page will get selected or some other area will be highlighted also. Does anyone know why this happens. An example url is http://sports.espn.go.com/mlb/index and it's also happening in a page I'm starting to convert to css layout and I want to know how to stop it. Thanks.